U.S. Pat. No. 6,188,040 granted Feb. 13, 2001 proposes a method of marking a translucent material object and a symbol reader for reading the symbol or code produced by such marking.
The symbol reader uses an illumination system comprising a plurality of light sources on one side of the object and a CCD camera on the other side of the object. A novel feature of the symbol reader is that the object is therefore illuminated by transparency and not by reflection.
U.S. Pat. No. 6,188,040 granted Feb. 13, 2001 addresses a particular application of the symbol reader to reading a symbol on a synthetic material ophthalmic lens or a molding shell for molding a synthetic material ophthalmic lens.
In developing this process, it has become apparent that it would be beneficial to be able to use the symbol reader to read a symbol on a pair of molding shells while they still have the molded ophthalmic lens between them, in order to be able to track the combination even before the ophthalmic lens is removed from the mold, although it should nevertheless be understood that it can be equally beneficial to read the symbol even before the ophthalmic lens is molded, when the molding cavity formed by the two molding shells is still empty.
In practise each of the two molding shells carries its own symbol, but because the two molding shells relate to the same ophthalmic lens it is sufficient to read off the symbol on one of them to determine the symbol on the other one.
For reasons of accuracy, the symbol is of course read off from the molding shell nearer the CCD camera.
However, because the illumination device operates by transparency, the problem arises that the symbol on the molding shell nearer the illumination device, which is the one at the greater distance from the CCD camera, may interfere with the reading, in particular due to the shadow it inevitably casts on the symbol that is being read.
A general object of the present invention is a simple and effective way to overcome this problem.
To be more precise, the present invention consists in a symbol reader for reading a symbol of any kind on an object of any kind, including an illumination system including a plurality of light sources on one side of the object and a CCD camera on the other side of the object, wherein the light sources of the illumination system are disposed on a circle on at least one circumference around an optical axis of the system and each light source is inclined to the optical axis, having an emission axis converging toward the optical axis on the same side as the CCD camera.
It is then possible to illuminate the symbol on the molding shell at the greater distance from the illumination system without illuminating the symbol on the molding shell nearer it, simply by bypassing the latter symbol.
U.S. Pat. Nos. 5,291,009 and 5,354,977 propose to read a bar code using a CCD camera and an illumination system in which each light source is inclined to the optical axis of the system.
However, the light sources lie in a plane, and are not disposed on a circumference of any kind.
In international patent application No. WO98/18098 at least some of the light sources of the illumination system lie on a circumference.
However, their emission axis is parallel to the optical axis of the system.
Furthermore, in both cases, the illumination system operates by reflection and not by transparency.
This is not the case in the symbol reader of the invention.
The features and advantages of the invention will become more apparent from the following description given by way of example and with reference to the accompanying diagrammatic drawings.